If a battery of the rechargeable type, such as a nickel-cadmium or manganese alkali battery, to name a few, is permitted to discharge completely, irreparable damage to the battery may result. In view of this the prior art has developed and at the present time many forms of monitoring devices are available to provide an indication, prior to complete discharge, of the condition of the battery serving as a power source of electrical equipment. Also, monitoring may be desirable to obtain information of battery condition so that upon a low supply voltage erroneous information from a powered circuit is not obtained. One such prior art battery monitoring device is disclosed in U.S. Pat. No. 3,550,105, which issued to Rinaldo De Cola and Irving I. Zook on Dec. 22, 1970.
Generally, the De Cola et al. device monitors the voltage of a battery by means of a flashing neon light. The rate of flashing of the light is controlled by the amplitude of voltage across and RC network which is directly proportional to the battery voltage. While devices of this type have been accepted as a means of providing an indication of battery condition, they suffer from the disadvantage that they have no provision to turn off the electrical equipment being supplied by the battery under conditions that the battery voltage falls below a safe operating level. Thus, in the known prior art, active preventive steps must be taken to obviate complete discharge of the battery following any alarm function.
The prior art is considered, also, to provide a further disadvantage, namely, that their monitoring circuits draw current at significant levels and that some devices require manual resetting after a trip condition. Further, some prior art devices require a reference source or device.